Variable sweep circuit



Sept 25, A1951 l. A. GREENWOOD, JR., ET Al. 2,559,164

VARIABLE sw'EEP CIRCUIT Filed Sept. 25, 1949 NGL@ DQT.

Sl 70A Zmventor /V/Q/V 0. GREENWOOD JR.

nu' JUL/AN a H/RSCH orneg Patented Sept. 25, 1951 UNITED STATES PATENT VARIABLE SWEEP CIRCUIT Ivan A. Greenwood, J r., Pleasantville, and Julian D. Hirsch, New` Rochelle, N. .Y.,. ,assignors to General Precision 'Laboratory.1ncorporated, a corporation of New York Applicationseptember 23, 1949; Serial No. 1173482 V9 Claims. (Cl. 25u-27) This invention relates to a variable sweep cirdegenerative. feedbackloop circuit in .whichthe cuit and more `speciiicallyto an improved cirgr-idswing is..substantially;zero over the..,-entire cuit for producinggan output potentalaof saw- 4range of thesweep pulse. andtherefore the Isweep tooth form. rateislinear.

YThe main purpose of the; present inventionis 5 VAnother fobjectf-is therefore to `provide any im.- tO provide aniniprOVed Sweep VCircuit ynew-*inge proved sweep generator capable ofproducing. a wide range of variation or sweep speed at constant sweep voltage which islinear within. very narrow amplitude for fanygiven triggering frequency. 11mm-,5.

.This circuitristcapableof producing a linear sweep f Another ,purpose is..L toA providek .such an imin which the peakrvoltageV is constant. In the l0 proved sweep.circuitfinwhich'the sweep speed present invention the maximum value .of the can be continuously varied `over .gwide. range `sweep voltage pulse is predetermined and this fwithoutaffecting the repetitionnrate orthe maxivalue is used asthereference level which determumsweep` voltage.

mines the termination of this pulSe- Still.another"objecty is vtoprovide--an improved Heretofore it hasebeenicommon to produce Saw- 15 circuit .of the type described. having e. ,pushfpuu `tooth waveforms ,by .thecuse of resistance-ca Output,

pacitance circuits. The main disadvantage of Other and further .objects .will .becomereadily this typeof previous circuit is that the voltage apparent from the.fcllrwvng.description when ISe With respeetlte `time iS epprexmately eX- considered in connectiony withrthe:l accompanying ponential in form. Other types of saw-tooth 20 `clrawingsfin,which;

WeiVe generators are known in which a sub- VFigure l is aschematiczcircuit diagram of a stantially linear rateis obtained but the range of sweep circuit in laccordance with the present the variation of the rate is limited. In these prior invention ;.V and devices the sweep cycle occupies substantially the Figure 2 illustrates vwan/@011,111 pmqluced,byV the entire triggering eyele per'ed, e Clipper being 25.generatoreofrthepresent invention.

utilized to discard the unwanted portion of the .-Generallyspeakingthepresent.inventioncomsweep voltage. Therefore it has been practically 4prises asweepcircuit which includes-a multiviimpossible to vary the sweep Speed independently breiter-.cagate generator which feedsesweepgenof the maXimum Voltage andtheirequencyof'the yeratorthe output of ^which is. connected to..a sweep pulsesl AISO. when Vthe repetition A'frevgecontrel unitwnienpdeterminesthe-peak of; the 'queney iS 10W'and retl'erge range of `control'is 'resweep voltage andl supplies-'a .control signal-.for quired.,V the range has to be changed' in steps and Vreturning the multivibrator. unitgto its quiescent the control of the rate'istherefore discontinuous. state. Asuitablefsource ofcontrolpulsesisuti- According toetheepresentA invention, a'predeterlized 4in a conventionalg manner totrigger :the mined maximum potential of thesweep voltage, 35 multivibrator circuit.` The multivibrator-feeds `which is variable,serves as the reference level. directly/31111;@ thejrsweepigenepatorz whichlincludes After the sweepvoltage reachesits predetermined -a @degenerative feedback'loopwdifferential` power maximum treturnsabruptlytoits minimum value Azadxnplier.,which providesf suitable 'push-pull ioutand remains there until thenext timinglpulse putJsWeep-voltages. l'Ehe high-feedback 4during initiates the next sweep cycle. The initiationfef 40 Vthe sweep gives excellent linearity. The control the sweep Vvoltagecyclesubstantially.coincides in unitcontrols-thernaximum-outputby supplying a time Wthrthe lirggeringpulee- The-SWeep1 Speed vcontrol pulsetoterminate the, gatingpulse fthus .or rate is determined. by the settingrof. the sweep cuttingoff.the.voltage supply-tothe timingQ-circircuit control. and the maximum voltageis preeuitfand returningA the`` multivibrator v.to-the quildetermined by .a control unitrconnectedltothe `45,escentstate. Ak "resistancecapacitance.circuit output of the sweep generator. connected to the-output of. the:differentialA am.-

, It will be readily apparent.Y that since-.the maxiplirler constitutes: thertiming.- circuit.

mum peakl voltage is used as the reference level, fAn illustrativerembcdiment fofsthe,present inthe voltage will reach this level quicker for high ventionrshown-inrthe schematic `diagram.of;lig. sweep speeds than for low sweep speeds. There- .50 I 1comprises.ailipflop*.multivibratorl or-gat'e fore the sweep speeds can becontinuously'varied generator, W-hichfincludes the triodes.. I I and; .I.2. over a very large portion of the periodjof the vv'Ihepentode 29.,.serx/,es as:a gateamplierfwhich `repetition frequency withoutv any variationv in feeds' a,.differential.amplif1er Icomprising ,the maximum voltage or frequency of the sweep -triodesr-i.and 39. .A control unit-comprisesthe pulses. The present invention utilizes .a lhigh-.gain diode 5 I andthefpent'ede 58. Anincorningrtrigger `is immaterial. "designed to utilize negative triggering pulses of pulse fed into the multivibrator energizes the timing circuit and initiates the sweep cycle and the control circuit terminates the timing cycle at the predetermined maximum value of the sweep voltage. The setting of the timing circuit determines the sweep speed or rate of increase of the sweep voltage. The sweep generator, in effect, constitutes a time delay circuit which supplies a pulse through the control unit to terminate the gate amplifier pulse and return the multivibrator to its quiescent state.

The cathodes of the multivibrator triodes II and I2 are connected together and -are biased through a common resistor 11. The control grid I3 of the triode II is connected through the resistor I4 and an anode resistor I6 to the positive side of a source of plate potential. The triode I I is normally biased above cutoi so that current ows in its anode circuit when no signal is being received. The voltage drop through the common cathode resistor I1 is suchthat under thiscondition the cathodes of the tubes I I- and I2 are about -22 volts above ground, so thata bias below cutoff is impressed on the triode I2 and during the quiescent state no current flows through the anode circuit of the tube I2.

i The input control signal for triggering the sweep generator may consist of either asingle pulse ora succession of pulses received periodically or aperiodically and the form of the pulses Preferably, the present circuit is action that transfers the multivibrator currentl .i -fromthe triode II to the triode I2. This regenlerative action is initiated when a triggering pulse causes reduction of the plate current-in the triode II which in turn reduces the voltage drop in the cathode resistor I1, Vthereby decreasing the negative bias on triode I2 and initiating anode current inthe latter tube. VWhen current ows through the anode circuit of tube I2 Vthe resulting potential drop through the resistor I6 lowers the potential of the anode 24 which is transmitted as a negative pulse through the condenser 23 to the grid I3 vthereby abruptly further decreasing the anode current through triode I I, which decrease of curlrent was initiated by the negative control pulse through the condenser 22. TheV recovery of the 'grid voltage I3 then takes place at a rate which is a function of the product of the capacitance 23 and its shunt resistance I4.- The grid I3 progressively returns to the potential of the anode 24 but the controlling time constant is large, so

that when using triggering frequencies of a few hundred cyclesper second orl less, the recovery 'time is much greater than the triggering period.

It will be readily understood from the above that since thetriode I I normally has current flowing through it, the interruption'of the flow of this current will result in an amplied'positive potential pulse at theanode 26 of the triode I I. This positive pulse is fed througha large coupling condenser 21 to the suppressorgrid 28 of the pentode gating amplifier 29. Normally this pentode is biased to cutoi, the bias being provided by connecting the grid 28 to the voltage divider 3 I. The

ycontrol grid 32 is given' a positive bias by being connected through the reSistor`33-to`fthe positive 4 side of the plate supply, but this positive voltage on the control grid 32 is not suicient to overcome the effect of the negative bias on the grid 28 so that normally no current flows through the anode circuit. The positive pulse fed to the suppressor grid 28 through condenser 21 initiates a current flow in the anode circuit of tube 29 producing a potential drop in the anode resistor 34 which potential drop in turn constitutes a negative signal which is impressed through resistor 36 on the grid 31 of the triode 38. The triode 38 together with Aoutput circuit of the triode. 4I. yThe cathode 52 the triode 39 constitutes a direct current diiierential amplifier, both of these tubes being normally biased slightly above cutoff.

Since the triodes 38 and 39 constitute a diierential amplifier, it will be understood that a negative signal applied to the grid of the triode 38 produces an amplified positive signal at its anode 4I and a similar signal of negative polarity at the anode 42 of triode 39. The negative signal from the anode 42 is fed through condenser 43 to control grid 32 of the high gain pentode 29. This circuit constitutes a degenerative feedback connection so that the small negative signal applied to the control grid 32 of the triode 29 results in a reduction of the negative potential that would otherwise be applied to the control grid 31 Aof triode38 through a resistor 36. Because the gain of the amplifier unit, comprising the pentode 29 and the triodes 38 and 39, is very high, only an extremely small change in the potential applied to the control grid 32.is necessary in order to cause a large change of potential at the anodes 4I and 42, respectively, of the triodes 38 and 39. Accordingly, since the vgrid. swing in tube 29 is very small, the latter operates on the linear portion ofV its curve and excellent linearity of the sweep voltage curve is provided. In effect, the output of tube 29 provides a source of substantially constant current that is used to charge the timing circuit, which includes the resistance 33 and the capacitance 43, and it is for this reason that the present circuit provides high linearity.

The anodes 4I and 42 of the triodes 38 and 39 are respectively coupled through condensers 46 and 41 to output terminals 48 and 49, which may be connected to any suitable utilization circuit. These two terminals can be used, if desired, as a push-pull output, such a push-pull output being @being that it does not substantially alter the focus of the cathode ray beam.

YAs previously mentioned, themaximum sweep voltage is maintained ata constant value and is used as a reference level with respect to which the termination of the sweep voltage is determined.

To this end, the diode5I is connected to the -nected to the control grid 51 of pentode 59 through the condenser 56. The anode 59 of the pentode 58 is connected by means of a condenser 6I to the control grid I9 of the triode I2. When ythe potential of the anode 4I of the triode 38 exceeds the value at which the diode 5I is biased, current flows through the 'diode and a positive pulse of potential is impressed .through the conv`denser 56 onto the grid-510i the pentode 58. The

ing -in the triode Il. vThe initiation of l anode current in the triode l I produces a potential/drop inthe anode resistor @QI-resulting in a negative pulse that istransmitted'though the condenser 21 to the grid 28 of the p entode 29, thereby terminating its gate and thus restoring-normal input `conditions to the differential; amplifier' triodesy38 and 39. .i

It will be readily seen from the vschematic diagram that the internal capacity'ofdiode 5| is efectively between one `r side of the pushpull -amplier output-and-ground. lnorder to produce *a i negative sweepsymmetrical with the positive sweep, a suitable condenser 55 is connected between the anode i2 of triode 39 and the cathode of diode I, the capacity of condenser 55 being of such value as to neutralize the effect of the internal capacity of the diode. This will cause the negative or return sweep Voltage curve to be of the same shape as that of the positive sweep.

The operation of this saw-tooth generator is illustrated in Fig. 2 wherein the time axis is the abscissa and the voltage is represented along the ordinate axis. The triggering control signal is represented as a recurring pulse having a period P. The slope of the front edge F' of the waveform, measured in volts per second, represents the sweep speed. It will be noted that the peak of the sweep voltage is constant, the maximum points constituting the reference level, as previously mentioned. By adjustment of either or both of the elements of the timing circuit, that is, the resistor 33 and the condenser 43, the slope of the curve F can be readily controlled. The left hand side of the edge F of the waveform coincides in time substantially with the control pulse. By varying the value of the resistor 33 or the condenser 43, or both, the length of time interval necessary for the sweep voltage to reach the maximum predetermined value represented at R, the latter value being determined by the diode limiter. It will be readily apparent that the faster the condenser charges the steeper willbe the slope of the front edge F and vice versa. In a practical embodiment of the present invention it was found that this slope could be varied over a range at least as great as 100 to 1 expressed in terms of volts per microseconds. This provides a range of control of at least 100 to 1. The termination of the gating pulse by the control unit is represented by the trailing side R of the sweep voltage curve.

It would be understood from the foregoing description that the present invention provides an improved saw-tooth generator in which the rate is always linear and in which the range of control is continuous. It will also be seen that a very large range of variation of sweep speed is possible and that the variation does not alter the peak voltage nor the repetition frequency. Although the present invention has been described in detail it will be apparent to those skilled in the art that changes can be made Without departing from the spirit of the invention.

Y claimed is:

Als'i'yeepf` circuit f'comprising a gate f generator,V a sweep. generator, z'circuit means i including afdegenerativefeedback loop! for controlling `the 'sweep "speedl of.A said sweep f generator and a' ccn- Ytrol funitifconnected 'lto the .output l .of said Vsweep generator, said control unit including an amplitude comparison 4circuit for [terminating VA'gating pulses'ifrom said gate'v generator.

' 1? vlsweepcircuitcomprising a, gategeneravtor,Maf-sweep!generator, a sourceof control sig.- lnaisLctninecteedto the. input of said .gate genera- `tor, the p'erio'd -of said L'gate generator. beingV at leastfaslong as r2 the period l of :the f control 'frequency, 1. circuit vmeans .including a degenerative Lfeedback Lloop1for-'icontrollingnthe sweep speed -g-ateigenerator.

fag-A sweepcircuit comprising "a gate generatorf.: aV sweep .generator having 1 ai relatively long period andbeingraadapted to fbe turned on by external control signals and to be turned off by a delayed signal initiated by one of said control signals, a degenerative feedback loop for controlling the sweep speed of said sweep generator, and circuit means including an amplitude comparison circuit connected between the output of said sweep generator and said gate generator for terminating sweep pulses from said sweep generator.

4. A sweep circuit comprising a gate generator, a sweep generator having a relatively long period and being adapted to be turned on by an external signal and to be turned oif by delayed signal initiated by said control signal. a degenerative feedback loop for controlling the sweep speed of said sweep generator, and a controlling unit including an amplitude comparison circuit connected to the output of said sweep generator for impressing a signal of predetermined value on said gate generator to terminate the operation of the latter.

5. A variable sweep circuit comprising, an electronic sweep generator of the negative feedback type, an electronic start-stop switch adapted for being turned on by an electric starting signal and adapted for being turned off by attainment of a predetermined sweep potential. a feedback connection from said generator to said switch for turning off said switch, and adjustable means in the negative feedback loop of said generator for varying the sweep speed thereof.

6. A variable sweep circuit comprising, an electronic sweep generator having a negative feedback loop having a push-pull output sweep potential, an electronic start-stop switch adapted to be turned oi upon attainment by said sweep generator of predetermined output sweep potential, a feedback connection from said generator to said switch for turning off said switch, a first generator output terminal for positive sweep potentials, a second generator output terminal for negative sweep potentials whereby a push-pull output potential may be secured to said first generator output terminal, and adjustable means in said negative feedback loop of said generator for varying the sweep speed thereof.

'7. A sweep circuit comprising a sweep generator including a gating amplifier and a pushpull amplier connected to the output of said gating amplifier, a timing circuit connected be- 7 tween the output of said push-'pull amplier and` said gating-amplifier and constituting a degenerative Afeedback loopcircuit'and an amplitude comparisonv circuit ,connected to .the output offv saidpush-pull `ampliiier for terminating the vfeedback through said degenerative timing circuit. ,c 8. A sweep .circuitcomprising a gate generator, a sweep generator, a, source of control sig- `nals connected to the input of said gate generator, the period of saidl gate generator being at least ,as long as the period of the control fre- 9. A sweep circuit comprising a gate generator, a sweep generator, a source of control signals .connected to the input of said gate generator,

the period of said gate. generator being at least iasclon'g vas'the period of the control frequency whereby said sweepl generator is triggered on by the control signals, said sweep generator including a gating amplifier and a power output amplier a timing circuit connected between the .output of said power output amplier and said gating amplier and constituting a degenerative feedback loop circuit for triggering off said gate generator, and an amplitude comparison circuit connected to the output of said second amplifier for controlling the termination of the feedback.

, IVAN A. GREENWOOD, Jn.

JULIAN D. HIRSCH.

` REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 2,414,486 Rieke Jan. 21, 1947 Mihel Jan. 25, 1949 

